Pilot performance depends on a number of factors including genetics, environment, age and health status. As a key component of health, nutrition plays a very important role in performance. It can affect the functioning of the nervous, endocrine and digestive systems. Our ability to respond to physiological stresses produced by influences such as altitude, temperature and trauma is influenced by our nutritional status. Our ability to cope with mental stresses also can be affected by nutritional status. This raises the question: what is “Optimum” nutrition? Optimum nutrition can be described as the intake of nutrients that lead to and maintain the highest possible level of health and performance. Our nutritional needs vary depending on age, sex, physical activity and stress. Factors which influence nutritional requirements include smoking, drinking, environmental pollutants and the use of medication.
The human body is a wonderfully complicated machine that is capable of synthesizing thousands of different chemicals from a calorie source (food) and 38 essential nutrients. A good diet should provide adequate amounts of calories to meet our energy needs and other components (amino acids and certain minerals) to maintain body structure. In addition, it must also provide an adequate supply of micronutrients, vitamins and minerals needed to maintain normal biochemical and physiological processes in our body.
In the early 1900s scientists believed that three compounds were needed to prevent dreaded diseases like scurvy and beriberi. They called these compounds “amines” and since they promoted life the prefix “vita” was added: vitamines.
Initially these compounds were used without understanding what they were or how they worked (mechanism of action). What was thought to be a single “vitamine” was actually many vitamins’ and numbers were added as subscripts to clarify their identification.
The fat-soluble vitamins (A, D, E and K) are found in fat-containing foods. They are absorbed into the body and stored in fatty tissue (adipose) and in the liver. Because they are retained in the body for considerable periods of time they do not require ingestion on a daily basis.
The water-soluble vitamins (C and all of the Bs) are stored for very short periods of time so they need to be replenished daily. Supplementary doses of these vitamins are acceptable and safe because they do not remain in the body very long. If more water-soluble vitamins are ingested than can be utilized by the body, the excess simply spills out into the urine.
Vitamin A – Retinol
This is the “vision vitamin,” essential to normal functioning of the retinal photoreceptor cells. It plays an important role in the regeneration cycle of “visual purple” (rhodopsin) which converts light stimulation of the visual cells into a neurological message that the brain interprets as “vision.”
A side effect of a deficiency in Vitamin A is night blindness, a reduced ability to see under reduced levels of illumination, The serious implications of reduced night vision performance are self-evident to the aviation community.
Vitamin A occurs in two forms: as carotene in green and yellow vegetables and yellow fruit and as converted vitamin A which is formed by other animals and incorporated into their products (milk, eggs)’. It is thought that certain products containing carotene or derivatives of vitamin A may be beneficial in promoting tissue healing and they have been proven effective in certain “dry eye” conditions.
BI – Thiamine
This vitamin is required for the normal functioning of the nervous system and the heart. Thiamine is found in vegetables, meats, and whole-grain breads and cereals. Deficiencies are rare in the US except in individuals who are chronic alcoholics.
B2 – Riboflavin
Riboflavin is important for metabolism. Deficiencies cause a drying of the lips, tongue and cornea (window of the eye). Any lesion that affects the cornea will adversely affect clarity of vision and make the individual more susceptible to glare and light sensitivity (photophobia). Riboflavin is widely distributed in meats, leafy vegetables and fish.
83 – Niacin
Important in metabolism and in keeping all tissue cells healthy, Niacin deficiency results in pellagra- a condition characterized by rough skin-mouth sores, diarrhea and mental changes. It is widely distributed in meat, beans, peas, poultry and whole grains. It is sometimes used medically to treat elevated cholesterol levels. It is now considered the first line of defense in the treatment of patients with high cholesterol.
B6 – Pyridoxine
B6 has three forms but all are used by the body in the same manner, to facilitate utilization of protein in maintenance of the nervous system, red blood cells, and metabolism. Deficiencies may therefore cause anemias or nervous disorders, including seizures or decreased sensation of touch. B6 is abundant in whole grain cereals, potatoes, red meat and yellow corn. Oral contraceptive pills may deplete the body’s stores of B6.
B12 – Cobalamine
Important in the formation of red blood cells and the proper functioning of the nervous and digestive systems. It occurs in lean meat, fish, milk, eggs and shellfish but is not found in plants. It is therefore imperative that strict vegetarians supplement their diets with this vitamin.
In any condition in which the red blood cells are affected, pilots must be cautious. The red blood cells are responsible for carrying oxygen throughout the body and any condition that may adversely affect the oxygen-carrying capacity of the blood is potentially dangerous to visual performance-particularly at pressure altitudes above 5000 ft. This condition is further aggravated by smoking because the carbon monoxide in cigarettes competes with oxygen in the red blood cells. The peripheral retina is the first vision element to be influenced by oxygen depletion; the symptom experienced would be a reduction in night vision and peripheral vision.
This is another B-vitamin component responsible for growth and metabolism. Deficiencies cause headaches, neurological damage and impaired ability toward off infections. Pantothentic acid is found in eggs, potatoes, whole grains and peanuts.
The last in the series of B-complex vitamins, biotin was once called Vitamin H. It too is important in metabolism. Deficiency syndromes of biotin have only recently been documented.
Vitamin C – Ascorbic acid
This least stable of the vitamins protects us from the oldest disease known to man, scurvy. Vitamin C deficiency weakens the walls of small caliber blood vessels (capillaries) and gives rise to symptoms of scurvy which include bruising, bleeding of the gums, anemia and poor wound healing. As early as the 16th century, American Indians knew that scurvy could be cured by drinking tea made from spruce or pine needles. Vitamin C has protective properties (antioxidants) similar to Vitamin E. Vitamin C is abundant in citrus fruits, leafy vegetables and potatoes.
Vitamin E – Tocopherols
Vitamin E is a vitamin that has received considerable attention for its antioxidant properties. In breathing oxygen for survival our bodies produce damaging oxygen by-products called free radicals (FR). These free radicals combine with the cell wall and interfere with the function and health of the cell. They may ultimately affect the function of an organ if enough cells are damaged. Antioxidants are suggested protective agents against free radicals. The medical implications of this are unlimited. Imagine all of our cells being protected from damaging agents implicated in cancer, the common cold, and the entire aging process.
The eye is a wonderful model for experimentation on this topic because it is directly exposed to oxygen and sunlight, both of which can generate free radicals. The cartoon model shown depicts how free radicals may damage cell walls and the protective action of vitamins and enzymes in such a scenario.
Vitamin D is called the sunshine vitamin because it is formed naturally by skin exposure to ultraviolet rays. It is also obtained from fish, milk, and margarine. A deficiency causes rickets, a deformation of the skeleton that produces bowed legs and a deformed spine. Vitamin D is a fat-soluble vitamin so it is stored for long periods in body tissue.
Required for normal clotting of the blood, hence deficiency causes hemorrhage and liver injury. However, deficiencies of this vitamin are uncommon, occurring mainly in isolated cases of antibiotic administration. Vitamin K is found in leafy vegetables. It is also available in synthetic form but requires a prescription.
This is water-soluble but large amounts are stored in the liver. It is important in the formation of normal red blood cells and in metabolism. It is present in green vegetables, beans, peas, yeasts, and liver. Deficiency, which occurs in alcoholics and patients taking certain anti-seizure medications, may produce anemia.
The minerals important to proper body functioning are calcium, magnesium, iron, selenium and zinc. Their primary functions are described at the end of Table 1.
The metabolic function of these vitamins and mineral are shown in Table 1. The causes and clinical symptoms of deficiency are briefly described in Table 2. A rather common cause of deficiency is low dietary intake. Among the other causes are malabsorption, impaired utilization and interaction with drugs. Certain life-style conduct also can put us in danger of developing specific micronutrient deficiencies. Smoking and alcohol consumption, for example, decrease micronutrient levels. Furthermore, certain segments in our population are vulnerable to nutritional problems. Classified as risk groups, these are shown in Table 3.
There are several micronutrients which play key roles in the visual function. They are listed in Table 4 along with associated visual disorders. The effectiveness of vitamin A in preventing night blindness was recognized long before its actual metabolism and function were understood. The importance of other vitamins and minerals in maintaining proper visual function has only recently been documented. The relationship of a micronutrient deficiency to the risk of developing certain major visual disorders and the therapeutic role of these micronutrients are now being recognized.
Research on the biochemical mechanisms involved in several types of visual problems continues in major medical institutions and universities. Sufficient evidence has been uncovered to implicate oxidative damage to the lipids as the underlying cause in disorders such as cataracts and age-related vision loss (macular degeneration). This would suggest that antioxidant micronutrients (which include vitamin C, vitamin E, beta carotene, zinc and selenium) may play an important role in minimizing the risk of suffering these age-related disorders. Current evidence does in fact show that those with higher levels of antioxidant micronutrients have a lower risk of cataracts. There is some scientific evidence that this may also be true for age-related vision loss (macular degeneration). Clinical trials are under way to test this relationship. Recent data support the view that if a disorder involves peroxidative (or free radical) damage, then the individual’s antioxidant status would be an important factor in determining the risk.
How do we minimize the risk of developing these age-related disorders (visual as well as others)? Will the so-called balanced diet provide adequate amounts of important nutrients, especially the antioxidant micronutrients? A balanced diet is presumed to provide adequate amounts of all the nutrients when caloric intake is adequate; but current evidence suggests that adequate caloric intake does not always assure sufficient nutrient in-take, especially with respect to the antioxidant micronutrients.
This then raises the issue of supplementation. In our opinion, it is prudent to make sure that one gets the recommended daily allowance (RDA) of all the micronutrients, with extra allowances for the antioxidant vitamins, keeping in mind that prevention is a better approach to enhancing the quality of life.
The aim of this article is to focus on the importance of the key micronutrients that could influence pilot performance. Acting on this current information, we can enhance the quality of our vision and our lives by adequate consumption of micronutrients. Europeans- and some Americans- of another era reinvigorated themselves by “taking the cure” at Baden-Baden or other fashionable watering spots. Perhaps some day we shall find the ultimate “cure,” ingesting an antioxidant “cocktail” that by the intake of micronutrients will protect our body tissues and optimize and extend our visual performance.
Dr. William Monaco